bg-image($url)
  @media screen and (-webkit-device-pixel-ratio :2)
    background-image url($url+"@2x.png")
  @media screen and (-webkit-device-pixel-ratio :3)
    background-image url($url+"@3x.png")

border-1px($bg)
  position relative
  &:after
    position absolute
    left 0
    bottom 0
    content ""
    display block
    width 100%
    height 1px
    background $bg
    @media screen and (-webkit-device-pixel-ratio :2)
      transform scaleY(.5)
    @media screen and (-webkit-device-pixel-ratio :3)
      transform scaleY(.33333)
